If the left arm (left subclavian artery) were involved, there would be very little chance that the brain would be involved. However, the right arm (right subclavian) artery has a different anatomy........one that comes off from a common source as the right common carotid artery (that leads to the brain). This common source is called the brachiocephalic artery. I evidently don't know all the details of your mom's case, but one of the most common causes of arterial embolism to the right arm are actually clots that originate in the left ventricular heart chamber secondary to a uninterrupted cardiac irregular heartbeat such as atrial fibrillation) and breaks off to travel there through a straight shot upwards.

If circulation is totally acutely blocked (as seems to be the case) to the right arm, blood thinners alone are inappropriate and there is no choice but to enter the right subclavian artery surgically directly by opening the artery or indirectly via threading an arterial catheter in order to remove the embolus.